Adult survivors of childhood leukemia are a growing population that have an excess in all-cause and cardiovascular (CVD)-related mortality and are at risk for multiple health problems, including CVD, osteoporosis, and obesity. Physical activity is protective and reduces risk for CVD, hypertension, Type 2 diabetes mellitus, and osteoporosis. The Lifestyle Physical Activity intervention has been efficacious in the general population in increasing sustainable levels of moderate-intensity physical activity and cardiorespiratory fitness and improving cardiovascular risk profiles and mental health. A targeted intervention tailored to the needs of leukemia survivors and intended to increase sustainable levels of moderate-intensity physical activity is not only warranted, but critical. It is imperative that methods to reduce morbidity and mortality of this young population while enhancing quality of life and productivity be addressed. The proposed study, Project ALLIFE (Acute Leukemia Lifestyle Intervention For Everyday), is a 12- month effectiveness trial with 120 young adult survivors of childhood leukemia randomized to either the Lifestyle Physical Activity intervention (ALLIFE-I) or a standard control group who will receive a periodic generic health newsletter (ALLIFE-SC). Major data collections will be at baseline, 6- and 12-months, with the two primary outcomes being levels of physical activity, as measured by 7-day physical activity recall, and cardiorespiratory fitness, as measured by the Aerobic Adaptation Test. Secondary outcomes will include other well-established measures of physical activity, cardiovascular risk profiles, gait and balance assessment, and psychological measurements. The primary research hypothesis to be tested is that the Lifestyle intervention will significantly increase physical activity and cardiorespiratory fitness in adult survivors of childhood leukemia in comparison with standard care. Three additional questions to be addressed are: determining if such an intervention leads to improvement in cardiovascular risk profile; determining if gait and balance disturbances are related to physical inactivity in leukemia survivors and if these disturbances improve with the intervention; and identifying factors that are predictive of improvement or lack of improvement in outcomes. This study will represent the first clinical trial aimed at increasing physical activity in leukemia survivors and will advance our understanding of this vulnerable population.